The present invention relates to a method of repairing an existing pipe, particularly to a method of repairing an existing underground pipe such as a gas pipe by reversing a flexible liner tube into the pipe.
There has been known a method of repairing an existing underground gas pipe by reversing a flexible liner tube into the pipe without trenching on road surface along the pipe. According to this method, at first a belt is introduced into an existing pipe so that one part of the belt is extending through the pipe over the entire length thereof, then another part of the belt is introduced into a flexible liner tube so that this part of the belt is extending through the liner tube along the entire length thereof. Afterwards, a necessary amount of adhesive agent is sealed into the liner tube, and one end of the liner tube is reversed so as to be fixed at one open end of the existing pipe. Subsequently, a pressurized fluid is applied from behind to continuously cause the reversal of the liner tube so that the liner tube may be introduced into the existing pipe. Such a reversal and introduction of the liner tube into the existing pipe can be effectively directed by pulling the above belt which has been in advance introduced into the existing pipe. In this way, the liner tube reversed in the existing pipe can adhere to the pipe internal surface by means of the adhesive agent and pressurized fluid.
The liner tube adhered to the internal surface of the existing pipe is usually made of a flexible gas-impermeable material, therefore it is effective in repairing any corrosion holes and is also effective in preventing any possible damages to the pipe due to an earthquake or the like. However, since the above method involves too many preparation steps before the operation of reversing and introducing a liner tube into an existing pipe, a time period required in the whole operation is relatively long and hence the cost for repairing an existing pipe is comparatively high.
In order to overcome the above problem, Japanese Patent Publication 61-20411 has suggested an improved method as shown in FIG. 7. In the method of FIG. 7, at first a leading block c is introduced into an existing pipe a through an open end b thereof, then an adhesive agent d is introduced into the existing pipe a. Subsequently, one end of a liner tube e is reversed so as to be fixed at the open end b of the existing pipe a. Afterwards, a pressurized fluid is applied from behind to continuously cause the reversal of the liner tube e so that the liner tube e may be introduced into the existing pipe a. In this way, the liner tube e can adhere to the internal surface of the existing pipe a by means of the adhesive agent d and pressurized fluid applied from behind.
In the method shown in FIG. 7, the leading block c is used to prevent the adhesive agent d from moving too fast so as to ensure that the internal surface of the existing pipe a may be coated with the adhesive agent d.
Although a method of FIG. 7 is allowed to dispense with some preparation steps before the operation of reversing and introducing a liner tube into an existing pipe, it is found to have some other problems as concluded in the following.
Firstly, the leading block c and the liner tube e have been proved difficult to pass through bent portions such as elbows along the existing pipe a. Particularly, a reversing/moving liner tube e is prone to stop in the pipe a, or the reversed liner tube e becomes deflected, as a result the liner tube e fails to properly adhere to the internal surface of the existing pipe a.
Secondly, if the leading block c encounters a pipe joint including a socket which usually has a larger diameter than pipe inner diameter, the leading block c is easy to get stuck in a such larger diameter portion. Consequently, the adhesive agent undesirably flows forward through gaps formed between the pipe internal wall and the leading block c.
Thirdly, since the adhesive agent is pushed forward by the reversing/moving liner tube e into which a pressurized pressure is applied from behind, the adhesive agent is apt to be excessively drawn into the space between the reversed liner tube e and pipe internal wall, or the air is easy to be introduced into the adhesive agent, resulting in improper adhesion between the reversed liner tube e and pipe internal wall.
Further, if the leading block c is pulled forward by a towing wire f, it is required that the wire f be in advance introduced into the existing pipe over the entire length thereof, and a towing apparatus is needed to pull the wire f so as to cause the leading block c to move forward. As a result, more equipment is needed and the repairing operation becomes complicated.
Moreover, since the adhesive agent d is pushed forward by the reversing/moving liner tube e, it is quite possible that an adhesive layer between the liner tube e and the pipe internal wall is uneven, resulting in uneven internal surface of the liner tube e adhered to the internal surface of the existing pipe a, as illustrated in FIG. 8A and FIG. 8B.